1. Field of the Invention
This invention is directed toward a vehicle with an improved suspension system.
The invention is more particularly directed toward a vehicle with an improved suspension system which incorporates two bogies.
2. Description of the Prior Art
Vehicles with a suspension system incorporating bogies on each side of the vehicle are well known. A bogie normally comprises a walking beam with a wheel at each end. The walking beam is pivotally mounted to the side of the vehicle chassis at about the longitudinal center of the beam. Bogies provide vehicles which are more suited for travel over rough and uneven ground since the pivoted walking beams of the bogies, on each side of the vehicle, allow the wheels mounted at the ends of the walking beams to have more vertical movement than if the wheels were mounted on axles traversing the chassis. Vehicles equipped with bogies thus provide a better ride on rough ground and are less liable to tip.
Known bogie-equipped vehicles usually have running gear arrangements that provide stability for the vehicle. A vehicle equipped with only a single bogie on each side is normally inherently unstable since the chassis is free to pivot relative to the walking beams. Thus bogie-equipped vehicles usually have at least two bogies on each side of the vehicle to provide stability, or one bogie is combined with at least one longitudinally spaced wheel or other type of running gear on each side of the vehicle, to provide stability.
Vehicles With a single bogie on each side of the vehicle are known. However, to provide stability to such vehicles, it is necessary to provide a mechanical cross-connection between the walking beams on the sides of the vehicle and the chassis. More particularly, a cross-beam is pivotally mounted at about its center to the chassis of the vehicle: The cross-beam is pivotally mounted to the chassis at about the longitudinal axis of the vehicle at the front or rear of the vehicle. The ends of the cross-beam are connected to the same ends of the two walking beams on the sides of the vehicle. The cross-beam arrangement prevents the chassis from uncontrollably tilting relative to the walking beams. The cross-beam arrangement also helps to stabilize the vehicle during operation. When one wheel at one end of a walking beam on one side of the vehicle passes over a bump, the one end of the walking beam is raised while the cross-beam tends to cause the corresponding end, and thus the wheel at that end, of the walking beam on the other side of the vehicle, to be automatically lowered. By the term "corresponding" end, it is meant the front end of the other walking beam if the one end of the one walking beam is the front end, or it is meant the rear end of the other walking beam if the one end of the one walking beam is the rear end. Of course, if the wheel on the corresponding end of the walking beam on the other side is already in contact with the ground, it is the chassis that is raised, due to its connection with the cross-beam. The raising of the chassis minimizes tilting of the vehicle, thus stabilizing its ride. At the same time, the cross-beam arrangement ensures good ground contact of all the wheels of the vehicle having two bogies, even when traversing very rough or uneven ground. An example of a two-bogie vehicle employing a mechanical cross-connection is shown in U.S. Pat. No. 3,313,555.
It is also known to have vehicles with a single bogie on one side of the vehicle. An example of such a vehicle is shown in U.S. Pat. No. 4,639,186. In this type of vehicle, two longitudinally spaced-apart wheels on the other side of the vehicle are fixed to the chassis. The vehicle thus always has at least three point ground contact and is stable. This type of vehicle has one side, the bogie side, which can more easily traverse rough ground while the vehicle is steered to have the other side, with the fixed wheels, pass over smoother ground.
The above known vehicles with a single bogie on one or both sides of the chassis, while providing a better ride over rough ground, have disadvantages. Those vehicles that employ a mechanical cross-beam to stabilize the vehicle, as shown in U.S. Pat. No. 3,313,555, have the cross-beam located in an unprotected area at the front or back of the vehicle. The cross-beam is thus in a position to be easily damaged when the vehicle is operated in a close-quarters environment such as when tree harvesting. Other vehicles, which employ a single bogie on one side, as shown in U.S. Pat. No. 4,639,186, do not provide as good a ride over rough, uneven ground as do vehicles with two movable bogies. Further, none of the above known vehicles, with a single bogie on one or both sides, have means for leveling the vehicle when it is in certain positions on sloping ground. If it is desired to have these vehicles leveled on sloping ground, separate leveling means would have to be added to the vehicle.